Genetic Engineering of Plants
The hurdle of creating successful genetically engineered plants in major crop varieties is now being overcome sequentially on a plant-by-plant basis. While plant genetic engineering has been successfully demonstrated in several model plant species, most notably tobacco, carrot and petunia, these species are not considered agriculturally important. Therefore, researchers have now directed their efforts toward improving commercially important crop plants through the use of genetic engineering (Potrykus, I., Annu. Rev. Plant. Physiol. Mol. Biol. 42: 205-225, 1991).
The term "genetic engineering," as used herein, is meant to describe the manipulation of the genome of a plant, typically by the introduction of a foreign gene into the plant, or the modification of the genes of the plant, to increase or decrease the synthesis of gene products in the plant. Typically, genes are introduced into one or more plant cells which can be cultured into whole, sexually competent, viable plants which may be totally transformed or which may be chimeric, having some tissues transformed and some not. These plants can be self-pollinated or cross-pollinated with other plants of the same or compatible species so that the foreign gene or genes carried in the germ line can be bred into agriculturally useful plant varieties.
Current strategies directed toward the genetic engineering of plant lines typically involve two complementary processes. The first process involves the genetic transformation of one or more plant cells of a specifically characterized type. The term "transformation" as used herein means that a foreign gene, typically in the form of a genetic construction, is introduced into the genome of the individual plant cells. This introduction is typically through the aid of a vector, which is integrated into the genome of the plant. The second process then involves the regeneration of the transformed plant cells into whole sexually competent plants. Neither the transformation nor regeneration process need be 100% successful, but must have a reasonable degree of reliability and reproducibility so that a reasonable percentage of the cells can be transformed and regenerated into whole plants.